Nitrocellulose propellant containing diffused linear polyester burning rate deterrent

ABSTRACT

Manufacture of burning rate deterrent coated propellants by contacting a nitrocellulose smokeless powder, at an elevated temperature, with a defined linear polyester of a new class of burning rate deterrents, which wets, and diffuses into the smokeless powder at the elevated temperature level, as a plasticizer therefor, but is substantially non-migrating within the smokeless powder at lower temperatures; effecting the contacting step under conditions causing the polyester to coat and penetrate the smokeless powder to form the coated propellant; and then reducing the temperature of the resulting deterrent coated propellant to the lower temperature above described. Also provided, are nitrocellulose smokeless powder propellants having as a burning rate deterrent, the defined polyester coating diffused by its own plasticizing action into the propellant to form a resulting burning rate gradient therefor.

United States Patent [1 1 Mellow 1451 July 3,1973

[ NITROCELLULOSE PROPELLANT CONTAINING DIFFUSED LINEAR POLYESTER BURNINGRATE DETERRENT [75] Inventor: Dale F. Mellow, Stanhope, NJ.

[73] Assignee: Hercules Incorporated, Wilmington,

Del.

[22] Filed: Sept. 3, 1971 21 Appl. No.: 177,813

[52] US. Cl 149/11, 149/10, 149/96, 149/98, 149/100, 149/94, 149/95 [51]Int. Cl C06b 19/02 [58] Field of Search 149/10, 11, 19, 96, 149/97, 98,99, 100, 94, 95

[56] References Cited UNITED STATES PATENTS 3,108,916 10/1963 Coffee eta1. 149/11 Primary Examiner-Carl D. Quarforth Assistant Examiner-P. A.Nelson Attorney-S. Grant Stewart et al.

[57] ABSTRACT Manufacture of burning rate deterrent coated propellantsby contacting a nitrocellulose smokeless powder, at an elevatedtemperature, with a defined linear polyester of a new class of burningrate deterrents, which.

Also provided, are nitrocellulose smokeless powder propellants having asa burning rate deterrent, the defined polyester coating diffused by itsown plasticizing action into the propellant to form a resulting burningrate gradient therefor.

11 Claims, No Drawings NITROCELLULOSE PROPELLANT CONTAINING DIFFUSEDLINEAR POLYESTER BURNING RATE DETERRENT This invention relates toimproved progressiveburning smokeless powder propellants, and to theirmanufacture. In one aspect this invention relates to a process,utilizing a new class of coating materials, as burning rate deterrents,for the manufacture of progressive burning smokeless powder propellantshaving improved burning rate gradient and ballistics properties. Otheraspects will be apparent in light of the accompanying disclosure, andthe appended claims.

It has been'general practice in the propellant art to regulate burningrate of propellants so as to produce high projectile velocities withoutincurring unduly high chamber pressures, by coating the propellantgrains with a deterrent material which will retard the initial burningrate of the grains. The practice has been particularly applied tosmokeless powder propellants. Well known procedures for coatingpropellants with burning rate deterrent materials are set forth in U.S.Pat. Nos. 2,147,698, 2,179,330, 2,198,746, and 2,187,866.

The deterrent coating materials utilized have been of two types, basedon their solubility in the propellant material, viz. the soluble, orplasticizer type, and the insoluble, or barrier type. The soluble, orplasticizer type, deterrent coating, due to its ability to plasticizethe propellant material penetrates the propellant grain so that as thepowder burns, the successively exposed surfaces contain gradually lessand less of the deterrent material thus causing the combustion of thegrain to proceed with increased speed along a substantially uniformburning rate gradient. However, although the plasticizer type deterrentcoating initially produces the desired burning rate gradient forrequisite progressive burning, those materials, during propellantstorage, continue to migrate throughout the propellant grain and, aftera period of time, they reach equilibrium concentration throughout thegrain and hence fail to provide for the requisite burning rate gradient.The barrier, or non-plasticizer type, does not penetrate the propellantmaterial and, although it does not migrate into the propellant duringstorage, it neveretheless fails to provide the progressivity of burningrequired for many applications. Various means have been proposed fordilution of the barrier type deterrents with materials soluble in thepropellant material to afford some degree of penetration and henceburning grade gradient, but they have been disadvantageous in numerousapplications, particularly when applied to the manufacture of small armspowders.

My invention is based on my discovery of a class of materials whichfunction as burning rate deterrents for smokeless powder propellants, toprovide broad uniform burning rate gradients without appreciablemigration of the deterrent material into the propellant particles duringstorage; and hence provide propellants having improved burning rategradient, and ballistics, stability.

In accordance with the invention a process is provided for themanufacture of burning rate deterrent coated propellants having improvedburning rate gradient and ballistics properties, which comprisescontacting a nitrocellulose smokeless powder, at an elevatedtemperature, with a linear polyester which is compatible with saidnitrocellulose, has a weight average molecular weight of from about1,500 to 30,000 and a melting point not exceeding about lF., which wetsand diffuses into said smokeless powder at said elevated temperature asa plasticizer therefor but is substantially non-migrating within saidsmokeless powder at lower temperatures; effecting said contacting underconditions causing said polyester to coat, and penetrate, said smokelesspowder to form said coated propellant; and reducing the temperature ofthe resulting coated propellant to a lower temperature above described.

The invention further provides nitrocellulose smokeless powderpropellants having a linear polyester as a burning rate deterrentcoating and diffused by its own plasticizing action into said propellantto form a resulting burning rate gradient therefor; said polyester beingcompatible with said nitrocellulose, having a weight average molecularweight of from 1,500 to 30,000, a melting point not exceeding l90F., andbeing substantially non-migrating within said smokeless powder attemperatures not exceeding about F.

The invention, in preferred practice, is directed to smokeless powderpropellants, and their manufacture, for small arms, and cannon, and tothe deterrent treatment of smokeless powders for caseless ammunitioncharges and other applications, including cartridge actuated, andnumerous other, industrial and military propellant devices.

Exemplary linear polyester burning rate deterrent materials utilized inpractice in the invention are those formed from dihydric alcoholcomponents such as ethylene glycol, polyethylene glycol, propyleneglycol, polypropylene glycol and neopentyl glycol, and dibasic acidcomponents such as adipic acid, azelaic acid, phthalic acid, and sebacicacid. Now preferred, are those polyester deterrent materials having aweight average molecular weight within the range of 1,500 20,000 asfurther illustrated herein. As a consequence of being compatible withthe nitrocellulose in the smokeless powder propellant, the polyesterdeterrent plasticizes the smokeless powder particle surfaces and remainsin the substantially non-migrating state of diffusion, without renderingthe propellant surfaces sticky or otherwise separating from the powderparticles.

When referring herein to nitrocellulose smokeless powders, it is meantsingle, double, and triple based smokeless powders well known in the-such as illustrated in U.S. Pat. No. 3,235,425.

Generally, the smokeless powder-polyester deterrent contacting, orcoating, step is carried out at a temperature within the range of 150212F. for a period of from 1 to 200 minutes, utilizing from 0.5 to 10weight percent of the polyester deterrent material, based on the weightof the uncoated smokeless powder.

The smokeless powder-polyester coating step is advantageously carriedout in the presence of water, the proportions of water being variableover a broad range. I have found that in accordance with proceduredescribed hereinabove utilizing water as a vehicle in an aqueous slurrycoating system such as that illustrated with reference to Example 2, theweight ratio of water to smokeless powder in the aqueous slurry can bein the range of from 1:1 to 20:1, more often at least as high as about4:1. On the other hand, a lesser proportion of water can beadvantageously utilized, generally without formation of an aqueousslurry as illustrated with reference to Example 1. In that embodiment, aweight ratio of water to the smokeless powder in the coating systemwithin the range of from about 0.05:1 to about 1:1, but more often notexceeding about 0.2: 1 is utilized. Thus, although the amount of waterutilized in these embodiments, is generally within the range of fromabout 0.05:1 to 20:1, the higher proportions within that range areapplicable to aqueous slurry coating systems.

1 have found that it is advantageous to introduce the polyesterdeterrent material into the coating step, when dissolved in asolvent-diluent therefor, which is not a solvent for the nitrocellulose,to lower viscosity and thereby facilitate uniform distribution of thepolyester material throughout the mass of smokeless powder. In thoseembodiments carried out in the presence of water, the solvent-diluentfor the deterrent is also characterized by low water solubility i.e., itis substantially water insoluble. Methylene chloride is a now preferredsolvent diluent; and other solvent diluents advantageously utilizedinclude benzene, diethyl ether and nbutanol. The solvent-diluentgenerally has a boiling point not exceeding about 125C. and issufficiently volatile that it can be readily evaporated from the coatingsystem. In other embodiments utilizing a diluent for the polyester to beintroduced into the coating system, the deterrent is introduced into thesystem as an aqueous emulsion, as an aqueous homogenized suspension, orin the case of a non-aqueous system is dissolved in a suitable volatilenon-aqueous solvent for the polyester, which is a non-solvent fornitrocellulose.

In accordance with one embodiment, a burning rate deterrent coatedpropellant of the invention is prepared by placing dry granularsmokeless powder, to be coated, in a mixing vessel equipped withagitation means, followed, optionally, by addition of water in an amountup to about 40 weight percent of the dry smokeless powder. From 0.5 toweight percent of the polyester deterrent coating material, based on theuncoated smokeless powder, is then introduced into admixture with thesmokeless powder and water if present, and is often advantageouslydissolved in a suitable diluent-solvent, which is not a solvent for thenitrocellulose in the smokeless powder, such as in methylene chloride inabout equal weight proportions. The mixture vessel is then closed andthe powder-polyester admixture is heated under constant agitation,generally by tumbling action, to 150 212F. and maintained at thattemperature for a period of from about l to 200 minutes.

At the end of the coating period, and with continued heating, thevessel, when methylene chloride or other volatile solvent-diluent forthe deterrent material, and- /or water is present, is opened andagitation is resumed to permit evaporation of the water and/or diluent,and drying of the resulting coated product until it becomes freeflowing, at which time heating is terminated for recovery of theresulting dried coated propellant product at ambient temperature forstorage.

In accordance with another embodiment of preparation of a deterrentcoated propellant of the invention, granular smokeless powder, to becoated, is slurried in a mix tank with water in a water: smokelesspowder weight ratio above described, more often from about 4:1 to :1,and the resulting slurry is maintained under agitation conditions whileadding the deterrent coating material thereto in an amount of from about0.5 to 10 weight percent based on the uncoated smokeless powder, thelatter optionally dissolved in a suitable diluent, such as methylenechloride as above described.

The resulting water slurry of deterrent coating material and propellantpowder is then heated during continued agitation to 150 212F. andmaintained at that temperature level for a period of from 1 to 200minutes to accomplish the required penetration.

At the end of the coating period the temperature of the water slurry ofcoated propellant product is reduced to below the storage temperaturelevel, generally below 150F., and the coated propellant product isremoved from the slurry and air dried to form free flowing coatedpropellant.

In accordance with conventional procedure, the dry coated propellantproduct can be glazed, cleaned, and blended, when necessary, to providethe requisite ballistics.

EXAMPLE 1 A granular double base smokeless powder having an averagegrain size of 0.65 inch (diameter) X 0.01 1 inch (length) was coatedwith a linear polyester having a weight average molecular weight ofabout 6,600, as a burning rate deterrent material of the invention.

Another portion of the same granular smokeless powder was similarlycoated with ethyl centralite, a well known plasticizer type burning ratedeterrent for propellants, to provide a control propellant forcomparative purposes.

The formulation of the double base granular smokeless powder to becoated, and the burning rate deterrent coating material utilized, areset forth in the following summary:

Granular Smokeless Powder Component Weight Percent Nitroglycerin 20.0Nitrocellulose 77.75 Diphenylamine 0.75 Barium Nitrate 1.50

Polyester Control Component Weight Ethyl Percent Centralite NeopentylGlycol 49.9

Adipic Acid 34.9

Palmitic Acid 15.0

Stearic-Oleic 0.3

Acid

ln carrying out the procedure for coating the smokeless powder with thepolyester buming rate deterrent, 10 pounds of the granular smokelesspowder was placed in the barrel of a jacketed tumbler vessel, togetherwith about 2 pounds of water; and 2 weight percent of the polyesterdeterrent material, based on the weight of the uncoated smokelesspowder, was then introduced into the smokeless powder-water admixture,as a 50 weight percent solution in methylene chloride as a diluenttherefor. The methylene chloride solvent is not a solvent for thenitrocellulose.

The barrel of the tumbler vessel was then closed, tumbling action wasinitiated, and heating fluid was circulated through the barrel jacket toincrease the temperature of the smokeless powder/water/polyesteradmixture to 2001F. The tumbling was then continued at 200F. for minutesduring which time coating action was complete to provide resultingcoated propellant product. At the end of the 90 minute period, thetumbling was terminated, the barrel was opened, and tumbling was resumedat the coating temperature level to 6 permit evaporation of the waterand methylene chlo- The PolyeslercBumins Rate eterr nt omponent WeightPercent ride to provide dry freeflowmg coated propellant prod EthyleneGlycol 29B uct. The tumbling action, and circulation of heating SebacicAcid 65.4 fluid through the jacket, were then terminated, and the CH-CHDlbasic 2.0 coated propellant product was then permitted to cool 5 FattyAcids to ambient temperature. unaccounted The above procedure wasutilized in preparation of the granular double base smokelesspowder-ethyl cenin carrying out the procedure, a suspension of thetralite control propellant, except that the ethyl cengranular smokelesspowder in 670 grams of water was tralite was applied without a diluenttherefor. formed in a mixing tank, equipped with agitation A series of10 of each of two separate portions of means. 2 percent of the deterrentcoating material, each coated propellant product was loaded afterprepabased on the weight of the uncoated smokeless powder, ration asshotgun cartridge components, and each sewas then added to the smokelesspowder/water suspenries of cartridges was fired, one series of eachcoated sion as a 50 weight percent solution in methylene chlopropellantbeing fired promptly after loading and the ride, under agitationconditions. After addition of the other after an extended storageperiod. Each coated deterrent material to the smokeless powder/watersuspropellant (product and control) contained 1.96 pension, thesuspension was heated to 85 90C. weight percent of the deterrentmaterial. Data summaunder continued agitation, after which the agitationrizing the firing tests are as follows: was continued, and thetemperature maintained at 85 Firing data After storage at Before storage2 140 F., 6 weeks Average Average Average maximum Average maximum muzzlechamber inuzzlo chamber (,l'anue in llurnin rate velocity, pressure,velocity, pressure, pressure, deterrent Shotgun L/s. 1 p.s.i. l'./s.p.s.i. p.s.i.

'lho polyester 12 gauge, 3"... 1, 221 11,000 1, 201 11,300 300 Ethyleentralite. .110 1, 2U!) 12, 200 1, 3-15 15, 700 +3, 500

l l"./s., throughout the specification, equals feet per second.

3 Before storage, herein, means within a 10-day period followingpreparation of the coated propellant.

The above data demonstrate substantially no penetration of the polyesterdeterrent material into the smokeless powder grains during storage, asevidenced by an actual decrease of 300 psi in average maximum chamberpressure, after storage. ()n the other hand, the data demonstrate ethylcentralite, a well known plasticizer type burning rate deterrent forpropellants, to have penetrated the smokeless powder grains duringpreparation, comparable to that of the polyester deterrent, but to haveseriously migrated into the smokeless powder grains, during storage, toimpair the original burning rate gradient with a resulting increase inaverage maximum chamber pressure of 3,500 psi.

The data demonstrate diffusion of the polyester deterrent into thesmokeless powder grains under coating temperature conditions, butsubstantially no migration at storage temperature levels, generally150F. or less, to be thereby substantially non-migrating during storageand provide for stable burning rate gradient and ballistics overprolonged periods.

EXAMPLE 2 Granular Smokeless Powder Component Weight PercenNitroglycerin 15.0 Nitrocellulose 84.15 Diphenylamine 0.85

EXAMPLE 3 The procedure of Example 1 was repeated except thatpreparation of the ethyl centralite formulation was omitted, theproportion of the polyester deterrent coating material utilized was 4.5percent (based on the weight of the uncoated granular smokeless powder)the coated propellant product was fired in each instance as a componentof a rifle cartridge, and the formulation of the smokeless powder to becoated was as follows:

Granular Smokeless Powder Component Weight Percent Nitroglycerin l0Nitrocellulose 88.25 Diphenylamine 0.75 Potassium Sulfate l .0

The coated propellant product contained 4.3 weight percent of thepolyester deterrent. These tests are further summarized as follows:

Firing Data Before Storage After Storage at 140F., 6 weeks Burning RateGun Average Average Average Average deterrent muzzle maximum muzzlemaximum velocity chamber velocity chamber f/s pressure f/s pressure ps1psi The Center- Polyester fire 3172 49 ,000 3237 49,500 of Ex. 1 RiffleThe data demonstrate an increase in average maximum chamber pressure ofonly 500 psi, a 1 percent increase, after 6 week storage period, ascompared with anjncrease of 10,500 psi, a 24 percent increase, observedfor the dibutylphthalate formulation of Example 6; and hence the markedstability of burning rate deterrent gradient over prolonged storageperiods, provided in accordance with the invention.

EXAMPLE 4 The procedure of Example 1 was repeated utilizing the samedouble base granular smokeless powder, except that the deterrent coatingmaterial was a polyester deterrent of the invention having a weightaverage molecular weight of about 1,600, and preparation of the ethylcentralite formulation was omitted. The following summarizes the tests:

EXAMPLE 5 The procedure of Example 1 was repeated utilizing the samedouble base granular smokeless powder, except that the deterrent coatingmaterial of the invention was a polyester having a weight averagemolecular weight of about 4,400, and preparation of an ethyl centraliteformulation was omitted. The summarizing data are as follow:

Firing Data As in the preceding examples, the above data demonstrate anincrease in average chamber pressure of 300 psi, a 2.6 percent increase,thus again demonstrating the stable burning rate gradients accomplishedin practice of the invention.

Firing data After storage at 140 F.,

Before Storage 6 weeks Average Average maximum maximum Average chamberAverage chamber Burning rate muzzle pressure, muzzle pressure, deterrentShotgun velocity, i./s. p.s.i. velocity, f./s. psi. The polyester 12gauge, 3". 1, 204 11, 300 1, 226 11, 900

1 See the followiu table:

g Weight Component: percent Ethylene glycol 16. Orthophthalic acid. 42.0 n-Oci anol 13. 4 n-l)ecan01 18.7 Adipic auitL. fl. 7 Sebauic acid 0. 1

EXAMPLE 6 The data demonstrate the improved stability of burn- Th f ll id t ill t Smokeless powder mg rate gradient accomplished in practice ofthe invenellants having well known burning rate deterrent maas shown yan Increase In average Chamber P terials of the soluble, or plasticizertype, and for com- Sure after g of y 600 P 3 53 Percent parativepurposes, a burning rate deterrent coated procrease. pellant of theinvention described hereinabove with reference to Example 3.

Firing data After storage at 140 F.,

Before storage 6 weeks Average Average Percent Average maximum Averagemaximum change in muzzle chamber muzzle chamber ballistics Smokelesspowder velocity, pressure, velocity, pressure, after component Deterrentcoating Gun 1' psi. f./s. p.s.i. storage Double base The polyester 01Examples 1 and 3 5.56 mm, centerlirc rifle. 3,172 4!), 000 3, 237 4.),500 1 Do! Dibutylplitlialate .do 3, 163 44, 600 3, 174 55, 100 23.6Single base DNT .30 06 ccnlerflrc rifle H. 2, 711 45,000 2, 866 55, 20022. 7 Double base Ethyl centralitc 12 gauge, 3 1, 229 12, 200 1, 345 15,700 28. 7

The footnotes 1-4:

Weight percent Nitro- Nitro- D1 phen- Weight Footnote glycerin cellulosevlamine B3(NO3)2 K2804 Deterrent coating percent il. 6 84. 4 0, 72 0.96The polyester of Example 3 4. 3 10.0 83. 0 0.75 Dibutylphthalate 6. 25 rI2. 0. 75 0.50 DNT t 6. 0 19.1) 76. 25 0. 74 1. 46 Ethylccntrnlitc A 1.(l6

The above demonstrate substantially constant ballistics obtained inpractice of the invention as compared with increase in average maximumchamber pressure of from 22.7 percent (DNT) to 28.7 percent (ethylcentralite) in the prior art compositions above.

The process embodiment of the invention utilizing an aqueous slurry typecoating step is advantageously applied to water cut smokeless powder,inasmush as it eliminates the need for removal of the water and residualsolvent from the smokeless powder, and air drying, prior to the coatingstep. The residual solvent-wet smokeless powder, still containing fromto 20 parts solvent per 100 parts of smokeless powder, generally amixture of ethyl alcohol and acetone in about equal volume proportions,is directly slurried with the water for the coating step, under whichconditions the warm water due particularly to its large volume, promptlyextracts the residual solvent from the smokeless powder to eliminate thepresence of that solvent during the coating step.

The invention provides for the active control of the penetration of theburning rate deterrent to accomplish a stable burning rate gradient.Thus, the diffusion of the burning rate deterrent into the propellant,and hence its plasticizing action, provides for a degree ofplasticization which increases with increase in each of time,temperature, and amount of coating material in the coating system; andthe penetration accomplished is preserved under storage conditions, anduntil use, due to the non-migration of the burning rate deterrent withinthe grains. Thus by correlating temperature, time, and amount of thedeterrent material in the coating system, a combination of coatingconditions can be readily determined for accomplishing any predetermineddegree of penetration, and for then locking in the deterrent to securethe resulting burning rate gradient for subsequent use.

As will be evident to those skilled in the art, various modificationscan be made or followed, in light of the foregoing disclosure anddiscussion, without departing from the spirit or scope of the disclosureor from the scope of the claims.

What I claim and desire to protect by Letters Patent is:

l. A nitrocellulose smokeless powder propellant having a linearpolyester as a burning rate deterrent coating diffused by its ownplasticizing action into said pro pellant to form a resulting burningrate gradient therefor; said polyester being compatible with saidnitrocellulose, having a weight average molecular weight of from 1,500to 30,000, a melting point not exceeding 190F., and being substantiallynon-migrating within said smokeless powder at temperatures not exceedingabout 150F.

2. A smokeless powder propellant of claim 1, wherein said burning ratedeterrent coating is a linear polyester formed from a dihydric alcoholand a dibasic acid.

3. A smokeless powder propellant of claim 2 wherein said dihydricalcohol is selected from the group consisting of ethylene glycol,polyethylene glycol, propylene glycol, polypropylene glycol andneopentyl glycol, and said dibasic acid is selected from the groupconsisting of adipic acid, azelaic acid, phthalic acid, and sebacicacid.

4. A smokeless powder propellant product of claim 2 containing saidpolyester in an amount of from 0.5 to

10 weight percent, based on the weight of said smokeless powder whenuncoated.

5. A smokeless powder propellant product of claim 4 wherein the averagemolecular weight of said polyester is within the range of from 1,500 to20,000.

6. A nitrocellulose smokeless powder propellant having an ethyleneglycol-sebasic acid resin as a linear polyester burning rate deterrentcoating diffused by its own plasticizing action into said propellant toform a resulting burning rate gradient therefor, and said smokelesspowder propellant containing said polyester in an amount of from 0.5 to10 weight percent based on the weight of said smokeless powder whenuncoated; said polyester being compatible with said nitrocellulose,having a weight average molecular weight of from 1,500 to 20,000, amelting point not exceeding 190F., and being substantially non-migratingwithin said smokeless powder at temperatures not exceeding about 150F.

7. A nitrocellulose smokeless powder propellant having an ethyleneglycol-adipic acid resin as a linear polyester burning rate deterrentcoating diffused by its own plasticizing action into said propellant toform a resulting burning rate gradient therefor, and said smokelesspowder propellant containing said polyester in an amount of from 0.5 to10 weight percent based on the weight of said smokeless powder whenuncoated; said polyester being compatible with said nitrocellulose,having a weight average molecular weight of from 1,500 to 20,000, amelting point not exceeding lF., and being substantially non-migratingwithin said smokeless powder at temperatures not exceeding about F.

8. A nitrocellulose smokeless powder propellant having an ethyleneglycol-phthalic acid resin as a linear polyester burning rate deterrentcoating diffused by its own plasticizing action into said propellant toform a resulting burning rate gradient therefor, and said smokelesspowder propellant containing said polyester in an amount of from 0.5 to10 weight percent based on the weight of said smokeless powder whenuncoated; said polyester being compatible with said nitrocellulose,having a weight average molecular weight of from 1,500 to 20,000, amelting point not exceeding F., and being substantially non-migratingwithin said smokeless powder at temperatures not exceeding about 150F.

9. A nitrocellulose smokeless powder propellant having a neopentylglycol-adipic acid resin as a linear polyester burning rate deterrentcoating diffused by its own plasticizing action into said propellant toform a resulting burning rate gradient therefor, and said smokelesspowder propellant containing said polyester in an amount of from 0.5 to10 weight percent based on the weight of said smokeless powder whenuncoated; said polyester being compatible with said nitrocellulose,having a weight average molecular weight of from 1,500 to 20,000, amelting point not exceeding 190F., and being substantially non-migratingwithin said smokeless powder at temperatures not exceeding about 150F.

10. A single base nitrocellulose smokeless powder propellant having alinear polyester as a burning rate deterrent coating diffused by its ownplasticizing action into said propellant to form a resulting burningrate gradient therefor, and said smokeless powder propellant containingsaid polyester in an amount of from 0.5

gradient therefor, and said smokeless powder propellant containing saidpolyester in an amount of from 0.5 to 10 weight percent based on theweight of said smokeless powder when uncoated; said polyester beingcompatible with said nitrocellulose, having a weight average molecularweight of from 1,500 to 20,000, a melting point not exceeding 190F., andbeing substantially non-migrating within said smokeless powder withintemperatures not exceeding about F.

2. A smokeless powder propellant of claim 1, wherein said burning ratedeterrent coating is a linear polyester formed from a dihydric alcoholand a dibasic acid.
 3. A smokeless powder propellant of claim 2 whereinsaid dihydric alcohol is selected from the group consisting of ethyleneglycol, polyethylene glycol, propylene glycol, polypropylene glycol andneopentyl glycol, and said dibasic acid is selected from the groupconsisting of adipic acid, azelaic acid, phthalic acid, and sebacicacid.
 4. A smokeless powder propellant product of claim 2 containingsaid polyester in an amount of from 0.5 to 10 weight percent, based onthe weight of said smokeless powder when uncoated.
 5. A smokeless powderpropellant product of claim 4 wherein the average molecular weight ofsaid polyester is within the range of from 1,500 to 20,000.
 6. Anitrocellulose smokeless powder propellant having an ethyleneglycol-sebasic acid resin as a linear polyester burning rate deterrentcoating diffused by its own plasticizing action into said propellant toform a resulting burning rate gradient therefor, and said smokelesspowder propellant containing said polyester in an amount of from 0.5 to10 weight percent based on the weight of said smokeless powder whenuncoated; said polyester being compatible with said nitrocellulose,having a weight average molecular weight of from 1,500 to 20,000, amelting point not exceeding 190*F., and being substantiallynon-migrating within said smokeless powder at temperatures not exceedingabout 150*F.
 7. A nitrocellulose smokeless powder propellant having anethylene glycol-adipic acid resin as a linear polyester burning ratedeterrent coating diffused by its own plasticizing action into saidpropellant to form a resulting burning rate gradient therefor, and saidsmokeless powder propellant containing said polyester in an amount offrom 0.5 to 10 weight percent based on the weight of said smokelesspowder when uncoated; said polyester being compatible with saidnitrocellulose, having a weight average molecular weight of from 1,500to 20,000, a melting point not exceeding 190*F., and being substantiallynon-migrating within said smokeless powder at temperatures not exceedingabout 150*F.
 8. A nitrocellulose smokeless powder propellant having anethylene glycol-phthalic acid resin as a linear polyester burning ratedeterrent coating diffused by its own plasticizing action into saidpropellant to form a resulting burning rate gradient therefor, and saidsmokeless powder propellant containing said polyester in an amount offrom 0.5 to 10 weight percent based on the weight of said smokelesspowder when uncoated; said polyester being compatible with saidnitrocellulose, having a weight average molecular weight of from 1,500to 20,000, a melting point not exceeding 190*F., and being substantiallynon-migrating within said smokeless powder at temperatures not exceedingabout 150*F.
 9. A nitrocellulose smokeless powder propellant having aneopentyl glycol-adipic acid resin as a linear polyester burning ratedeterrent coating diffused by its own plasticizing action into saidpropellant to form a resulting burning rate gradient therefor, and saidsmokeless powder propellant containing said polyester in an amount offrom 0.5 to 10 weight percent based on the weight of said smokelesspowder when uncoated; said polyester being compatible with saidnitrocellulose, having a weight average molecular weight of from 1,500to 20,000, a melting point not exceeding 190*F., and being substantiallynon-migrating within said smokeless powder at temperatures not exceedingabout 150*F.
 10. A single base nitrocellulose smokeless powderpropellant having a linear polyester as a burning rate deterrent coatingdiffused by its own plasticizing action into said propellant to form aresulting burning rate gradient therefor, and said smokeless powderpropellant containing said polyester in an amount of from 0.5 to 10weight percent based on the weight of said smokeless powder when coated;said polyester being compatible with said nitrocellulose, having aweight average molecular weight of from 1,500 to 20,000, a melting pointnot exceeding 190*F., and being substantially non-migrating within saidsmokeless powder at temperatures not exceeding about 150*F.
 11. A doublebase nitrocellulose smokeless powder propellant having a linearpolyester as a burning rate deterrent coating diffused by its ownplasticizing action into said propellant to form a resulting burningrate gradient therefor, and said smokeless powder propellant containingsaid polyester in an amount of from 0.5 to 10 weight percent based onthe weight of said smokeless powder when uncoated; said polyester beingcompatible with said nitrocellulose, having a weight average molecularweight of from 1,500 to 20,000, a melting point not exceeding 190*F.,and being substantially non-migrating within said smokeless powderwithin temperatures not exceeding about 150*F.